Deterministic unit conversion reproducing NIST SP 811 exact factors (length, mass, volume,

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xa3091005a76b1480F1897a9D0C2e1c55B7767674",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "1000",
    "maxTimeoutSeconds": 300
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "method": "GET",
        "queryParams": {
          "from": "nautical_mile",
          "to": "meter",
          "value": 1
        },
        "type": "http"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "input": {
          "additionalProperties": false,
          "properties": {
            "method": {
              "enum": [
                "GET",
                "HEAD",
                "DELETE"
              ],
              "type": "string"
            },
            "queryParams": {
              "properties": {
                "from": {
                  "description": "source unit (name or alias, e.g. mile, kg, °C)",
                  "type": "string"
                },
                "to": {
                  "description": "target unit (same dimension)",
                  "type": "string"
                },
                "value": {
                  "description": "quantity to convert",
                  "type": "number"
                }
              },
              "required": [
                "value",
                "from",
                "to"
              ],
              "type": "object"
            },
            "type": {
              "const": "http",
              "type": "string"
            }
          },
          "required": [
            "type",
            "method"
          ],
          "type": "object"
        },
        "output": {
          "properties": {
            "conversion_factor": {
              "type": "number"
            },
            "dimension": {
              "type": "string"
            },
            "exact": {
              "type": "boolean"
            },
            "from": {
              "type": "string"
            },
            "op": {
              "type": "string"
            },
            "result": {
              "type": "number"
            },
            "source": {
              "type": "string"
            },
            "to": {
              "type": "string"
            },
            "value": {
              "type": "number"
            }
          },
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

curl "https://touchstone.locomot.io/unit"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://touchstone.locomot.io/unit");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

import httpx
res = httpx.get("https://touchstone.locomot.io/unit")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header